The Airflow Perturbation Deviie (APD) to measure resiratory airways resistance will be tested to give assurance of validmeasurements. The APD will then be used to measure airways resistance on humans who are exercising until they reach their minimum exhalation times. Concurrently, modeling will continue to predict exhalation time during exercise. Correlation of minimum exhalation time with conventional pulmonary function data will be attempted.